A station on a WLAN needs to periodically leave an operating channel used by the access point for the WLAN to scan for other devices. In so doing, the WLAN station can switch to another channel for a short amount of time and then return to the operating channel, resulting in an absence period during which the WLAN station is absent from the operating channel. In order to avoid data loss, the WLAN station must inform the access point of its absence from the operating channel so that the access point does send not data to the WLAN station on the operating channel during the absence period.
In present WLANs, a station can inform the access point in advance of each absence period by setting a power management (PM) bit in a data frame sent to the access point. The WLAN station can then wait to receive an acknowledgement from the access point and, after receiving the acknowledgement, can wait for an additional period to allow the access point to register the station's new mode before leaving the channel. After completing the scan, the station can return to the operating channel and send another data frame with the PM bit set to 0 to the access point to inform the access point that the station has returned to the operating channel. In this regard, present WLAN stations inform WLAN access points in advance of leaving for each absence period with a first message and upon returning from each absence period with a second message.
The overhead involved in the station informing the access point of leaving for and returning from an absence period can be burdensome to both the WLAN station and access point. Further, the signaling involved can consume over-the-air interface resources that can impact other devices on the WLAN. In many instances, the time needed for notifying the access point and waiting for an acknowledgement in advance of each absence period can be as long as, or even longer than the actual absence. As such, present methodologies in which a station notifies an access point in advance of leaving for and upon returning from each individual absence period are inefficient and overhead intensive.